Electronic devices are commonly used in several applications. In the particular case of power electronic devices, they are constructed so as to be able to withstand an operation power of relatively high value (for example, of the order of 100-625 W).
The electronic devices are generally integrated on chips of semiconductor material. Each chip is then housed into a proper package, which protects the chip at the same time allowing the access to its terminals. The package comprises an insulating body that embeds the chip. The insulating body exposes several leads, each one of them being connected electrically to a correspondent terminal of the chip; typically, the lead is connected to the terminal of the chip with a wire-bonding technique, wherein a conductive wire is fastened at an end thereof on the lead and at another end thereof on the terminal of the chip. The leads of the package are used to connect the same (and then the corresponding terminals of the chip) to external circuits. For this purpose, the electronic device is generally mounted on a Printed Circuit Board (PCB). For example, in the Surface-Mount Technology (SMT) the leads are provisionally attached, by means of solder pastes, to corresponding conductive tracks of the printed circuit board through a light pressure (pick and place), and they are then soldered by reflow thereon.
The power electronic devices are subject to remarkable heating during their operation (since they are affected by high currents and/or voltages, of the order of 50-1,500V and 0.1-8 A, respectively). Therefore, the package of every power electronic device is generally provided with one or more heat sinks Particularly, a main heat sink has a wide surface exposed on a surface for mounting the insulating body on the printed circuit board; the chip is fastened on the main heat sink, so as to facilitate the transfer of the heat produced by it to the outside of the package (so as to reduce the thermal resistance of the electronic device from its chip to the external atmosphere). The main heat sink may also be connected electrically to a terminal of the electronic device integrated on the chip, so as to act as a corresponding lead as well—for example, when the electronic device has a vertical structure with such terminal made on a back surface of the chip that is fastened on the heat sink (while the other terminals of the chip, made on a front surface thereof, are connected to the corresponding leads through conductive wires). In addition, an auxiliary heat sink has a wide surface exposed on a free surface of the insulating body (opposite its mounting surface); the auxiliary heat sink is mounted on the chip to increase the transfer of the heat produced by it to the outside of the package (so as to further reduce the thermal resistance of the electronic device from its chip to the external atmosphere). The auxiliary heat sink may also be connected electrically to another terminal of the electronic device integrated on the chip (made on its front surface).
A typical application of the power electronic devices is in the switching systems. A generic switching system comprises one or more pairs of power electronic switches (for example, power transistors of MOS type); every pair of power transistors is connected in a half-bridge configuration, wherein the transistors are arranged in series (in order to be connected between a reference terminal, or ground, and a power supply terminal), with a common node thereof that defines an output terminal for the connection of a load. The power transistors are turned on and turned off alternatively (with a short dead time at every switching wherein they are both off).
The power transistors are generally integrated on distinct chips (because of either technical or economic reasons), which chips are then housed in corresponding packages. Therefore, the switching system comprises a distinct package for each power transistor, which is mounted separately on the printed circuit board (which implements the desired electrical connection between the different power transistors).
However, the known structures of the switching systems are not completely satisfactory—for example, with respect to their size, to their constructive complexity, and to their thermal dissipation effectiveness.